1. Field of the Invention
The present invention relates to an optical member for biological information measurement, a biological information calculation apparatus, a biological information calculation method, a computer-executable program, and a recording medium for calculating noninvasively glucose, cholesterol, urea, triglyceride, protein, and the like in body fluid by measuring a living body tissue optically.
2. Related Art of the Invention
A conventional optical measuring instrument for measuring a specific component in a living body or a solution will be described.
There exists an optical measuring instrument for measuring a blood glucose level with making upper and lower lips adhere to a transparent attenuated total reflection element having a pair of reflecting surfaces facing each other in parallel (hereafter, referred to as an ATR prism) (e.g., refer to Japanese Patent Laid-Open No. 97-113439). It is assumed that this conventional optical measuring instrument is called first conventional art.
More specifically, as shown in FIG. 12 which is a view of a conventional optical member for biological information measurement, light is injected in an ATR prism 1201 from an optical fiber 1202 in the state of holding the ATR prism 1201, which is constituted of selenium zinc, silicon, germanium or the like, in a mouth to press down the ATR prism 1201 by the lips 1203.
Then, light which repeatedly performs total reflection on boundaries between reflecting surfaces of the ATR prism 1201 and lips 1203 with infiltrating into the lips 1203 slightly (i.e., performs attenuated total reflection), and is emitted to the outside of the ATR prism 1201 is taken out and analyzes using an optical fiber 1204. Thus, it is possible to know how much the light at each wavelength is absorbed by the specific component by analyzing the light spectrum of the emitted light and calculating the amount of the light at wavelengths which the specific component which is the measuring object tends to absorb. In this way, it is possible to measure quantitatively the specific component in a living body.
In addition, there is an optical measuring instrument for measuring a blood glucose level and a blood ethanol concentration by injecting a laser beam with a wavelength of 9 to 11 μm is into this ATR prism after making the ATR prism, which is constituted of ZnSe crystal, or the like, adhere to mucosae of lips, performing multipath reflection inside the ATR prism, and analyzing attenuated total reflection light, scatter reflection light, and the like (i.e., refer to Hideo Fukushima, et al., “Non-invasive mensuration technique—development of optical glucose sensor of blood glucose level—”, BME, Japan Society of Medical Electronics and Biological Engineering, 1991, vol. 5(8), p. 16-21). It is assumed that this conventional optical measuring instrument is called second conventional art.
The light which proceeds to the inside of the ATR prism is reflected after infiltrating into lips slightly.
The reflected light receives the influence of each component in body fluid which exists in lips, and decreases more than before infiltrating into lips.
Then, it is possible to obtain information on each component in the body fluid by measuring the light amount of the reflected light.
The first and a second conventional art apply an evanescent wave (being the so-called seeping light) to a quantitative analysis.
In addition, there exists a contact for biological information detection including abutting means of having a concave portion abutting against the living body tissue, detected-light emission means of emitting detected light from a part of the concave portion, and detected-light incident means which is provided in another part of the concave portion and is injected with the detected light, wherein the abutting means is constituted of a material which has a refractive index higher than a refractive index of a living body tissue, and wherein the detected light is injected into the detected-light incident means in the state that the abutting means and living body tissue abut each other after passing the living body tissue which is wrapped up in the concave portion (e.g., refer to National Publication of International Patent Application No. 2001-058355). It is assumed that this conventional contact for biological information detection is called third conventional art.
There are few damages to a living body tissue, and it is possible to measure biological information easily and highly accurately.
Nevertheless, also in the first to third conventional art, light from other than a light source for measurement such as sunlight and light from illumination may constitute disturbance light in many cases.
Thereby, the above-mentioned conventional art has a subject that an adverse effect to biological information measurement by disturbance light may arise.
In addition, in the first and second conventional art, the seeping depth d of an evanescent wave filtrating into a living body can be obtained as follows:
                    d        =                              λ            0                                2            ⁢            π            ⁢                                                                                n                    1                    2                                    ⁢                                      sin                    2                                    ⁢                                      θ                    1                                                  -                                  n                  2                  2                                                                                        (                  Formula          ⁢                                          ⁢          1                )            
d: Penetration depth
λ0: Wavelength in vacuum
n1: Refractive index of first medium
n2: Refractive index of second medium
θ1: Incident angle from first medium to second medium
With computing the case that λ0=10 μm and θ1=45° using ZnSe crystal (n1=2.0) as the ATR prism, since a refractive index of a living body is approx 1.3 to 1.5, d becomes 29 μm at the time of n2=1.41, and hence, it turns out that it is possible to obtain the information with regard to the state of approx tens of μms of surface and its vicinity.
Here, an electric field of the evanescent wave exponentially decreases according to the depth.
Hence, it is very important to make the living body tissue adhere to the living body tissue measuring section of the ATR prism.
Nevertheless, in both the first and second conventional art, the ATR prism is just held or is just pressed in lips.
Therefore, it is hard to make lips adhere to the ATR prism.
For this reason, in the first and second conventional art, the accurate measurement of biological information may become hard.
In addition, although it becomes possible in the third conventional art to upheave the living body tissue to the formed concave portion, and to measure selectively a region which is upheaved, similarly to the above-mentioned first and second conventional art, the adhesion of the living body tissue and living body tissue measuring section is very important.
Nevertheless, since the adhesion of the living body tissue and living body tissue measuring section is hard, when the adhesion of the living body tissue and living body tissue measuring section is insufficient, optical path length may vary, and the accurate measurement of biological information may become hard.
In consideration of such conventional subjects mentioned above, the present invention aims at providing an optical member for biological information measurement, a biological information calculation apparatus, a biological information calculation method, a computer-executable program, and a recording medium which can suppress the adverse effect to biological information measurement by disturbance light.